docs: def _employer_phase(self):
          '''Iterates through the employer bees and merges each with another
          random bee (one value is moved in accordance with the second bee's
          value); if the mutation performs better, the bee is moved to the new
          position
          '''
  
          self._logger.log('debug', 'Employer bee phase')
          modified = []
          for bee in self._employers:
              if self._processes <= 1:
                  new_values = self._merge_bee(bee)
                  self._move_bee(bee, new_values)
              else:
                  modified.append((
                      bee,
                      self._pool.apply_async(self._merge_bee, [bee])
                  ))
          for pair in modified:
              self._move_bee(pair[0], pair[1].get())